Among other changes at the network: “Meet the Press” anchor Chuck Todd will anchor a daily political news show in the afternoons. “The Ed Show,” anchored by Ed Schultz and “Now with Alex Wagner” were cancelled. Former NBC “Nightly News” anchor Brian is also expected to play a prominent role.

The new strategy is meant to help MSNBC get out of the ratings doldrums. In a memo to staff, MSNBC President Phil Griffin said Mr. Sharpton had done a “terrific job bringing his voice and a big spotlight to issues of justice, civil rights and equality.”

“PoliticsNation” will have its last weekday broadcast next Friday, Sept. 4 and will relaunch on Sundays on October 4.